This invention is related to a breathable elastomeric film made from high performance elastomers such as styrenic block copolymers and filled low performance elastomers such as polyolefins, and a soft, breathable elastic laminate comprising said breathable elastomeric film and a nonwoven web. The laminate is particularly useful as an outer cover for disposable diapers and other disposable personal care products, and for breathable surgical gowns and other breathable by applications. In addition, this invention is directed to a method for producing such films and laminates.
The present invention is directed to breathable elastomeric films and nonwoven materials and laminates thereof. Such laminates have a wide variety of uses, particularly in the areas of limited use and disposable items.
Films have been traditionally used to provide barrier properties in limited use or disposable items. By limited use or disposable, it is meant that the product and/or component is used only a small number of times, or possibly only once, before being discarded. Examples of such products include, but are not limited to, surgical and health care related products such as surgical drapes and gowns, disposable work wear such as coveralls and lab coats, and personal care absorbent products such as diapers, training pants, incontinence garments, sanitary napkins, bandages, wipes and the like. In personal care absorbent products, such as infant diapers and adult incontinence products, films are used as the outer covers so as to prevent body wastes from contaminating the clothing, bedding and other aspects of the surrounding environment of use. In protective apparel, such as hospital gowns, films are used to prevent cross-exchange of microorganisms between the wearer and the patient.
Although these films are generally effective barriers with respect to water vapor and the like, they are not aesthetically pleasing because their surfaces are smooth and either feel slick or tacky and they are visually unappealing, making them less desirable in apparel applications and other uses where they are in contact with human skin. Thus, it is desirable that these items be more cloth-like, both from a tactile and visual standpoint. It is also desirable for an outer cover material to possess stretch and recovery properties to provide better fit and comfort. It is particularly desirable that the stretch and recovery properties be biaxial to accommodate the movement of the wearer in different directions.
Laminates of films have been used to create materials which are both impervious and somewhat cloth-like in appearance and texture. One example of such a laminate is the outer cover on disposable diapers. A primary purpose of the film in such laminates is to provide barrier properties. However, there is also a need that such laminates be breathable so that they can transmit water vapor which, in turn, requires that the film be breathable. Apparel made from laminates of breathable or microporous films are more comfortable to wear because they reduce the water vapor concentration and the consequent skin hydration underneath the apparel item.
There are a number of known ways of making a film breathable including aperturing and the use of fillers. Breathable polyolefin films can be produced by stretching a precursor film filled with a filler such as calcium carbonate particles. Breathable films which are gas/vapor permeable and liquid impermeable are taught by U.S. Pat. No. 4,472,328 to Sugimoto et al. The Sugimoto et al. patent teaches a breathable polyolefin film prepared from a polyolefin/filler composition having from 20 percent to 80 percent by weight of a filler such as a surface treated calcium carbonate. A liquid or waxy hydrocarbon polymer elastomer was found to produce a precursor film that could be monoaxially or biaxially stretched to make the film breathable. U.S. Pat. No. 4,777,073 to Sheth teaches a breathable film produced from a precursor film that is prepared from a polymer composition comprising at least one polyolefin component and a filler. Suitable polyolefins for film production are indicated to include polypropylene, copolymers of propylene, homopolymers and copolymers of ethylene or blends thereof. Suitable fillers are indicated to be any organic or inorganic material having a low affinity for and a significantly lower elasticity than the polyolefin component, or no elasticity at all, preferably a rigid material having a non-smooth hydrophobic surface or a material which is treated to render its surface hydrophobic.
Laminates or composites of breathable films and nonwoven materials are taught by U.S. Pat. No. 5,695,868 to McCormack. The laminates or composites are made from a breathable film which is stretch-thinned and bonded to a fibrous polyolefin nonwoven web.
PCT International Patent Publication No. WO 99/14044 teaches a soft, breathable elastic laminate comprising a water vapor impermeable, or water vapor mu permeable, elastic film material loaded with a filler having a particle size suitable for pore formation and a nonwoven web bonded to the elastic film, the film being stretched in at least two directions. The stretching of the film renders the film microporous and, thus, breathable, or, in the case of films which are initially breathable, more breathable. The breathable elastomeric film is a metallocene-catalyzed polyethylene polymeric resin material comprising a filler material of at least 10% by volume of the film. The metallocene-catalyzed polyethylene polymeric resin material has a density of from about 0.850 to about 0.917 g/cc, and the film comprises from about 10% by volume to about 50% by volume filler. Although having good elastic properties, a film having better elastic properties than metallocene-catalyzed polyethylene elastomers is desirable.
One such film is disclosed by U.S. Pat. No. 5,733,628 to Pelkie which teaches breathable, elastic polymeric film laminates employing apertured films made from high performance elastomeric materials such as styrene block copolymers.
One problem which has been found when using filled elastomers for producing breathable stretch-thinned films is the tendency of the micropores formed during the stretch-thinning process to close up upon release of the stretching force due to the elastic recovery properties of the elastomers. This is particularly true of high performance elastomers like styrene block copolymers. As a result, there has always been a tradeoff between breathability and stretch and recovery properties for stretch-thinned filled elastic materials.
Accordingly, it is one object of this invention to provide a film capable of high breathability and high elastic stretch and recovery once it is stretch-thinned.
It is another object of this invention to provide a film having high breathability and high elastic stretch and recovery which is capable of high biaxial stretching.
These and other objects of this invention are addressed by a breathable elastic film comprising a blended or compounded product formed by blending or compounding a high performance elastomer and a filled low performance elastomer, the filler including a plurality of particles suitable for forming pores in the film upon stretch-thinning of the film. In accordance with a particularly preferred embodiment of this invention, the high performance elastomer is a styrenic block copolymer and the low performance elastomer is a polyolefin. Upon stretch-thinning of the film, micropores are formed by the low performance elastomer portion of the film. In accordance with one embodiment of this invention, the high performance elastomer is also filled with particles suitable for pore formation whereby, upon stretch-thinning of the film, micropores are formed by both the high performance elastomer portion and the low performance elastomer portion of the film. The microporous stretch-thinned film of this invention demonstrates both high breathability as well as elastic stretch properties greater than 100 percent and recovery.
In accordance with one embodiment of the invention, the microporous film is laminated to a fibrous layer. The fibrous layer can comprise a nonwoven web such as, for example, an extensible nonwoven web. Film/nonwoven laminates of the present invention can be used as a barrier layer in personal care articles such as, for example, as outer covers in diapers, adult incontinence garments, protective apparel and the like. In addition, the breathable microporous films and/or film laminates of this invention can comprise a component of an absorbent bodily article. As one example, an absorbent bodily article can comprise a liquid pervious liner; an absorbent core; and a microporous film or film laminate of this invention wherein the absorbent core is positioned between the liquid pervious liner and microporous film or film laminate.
The films of this invention are produced by blending or compounding a high performance elastomer with a low performance elastomer, at least one of which is filled with particles suitable for pore formation upon stretching of the film, forming a blended or compounded product, forming the blended or compounded product into a filled film and stretch-thinning the film, forming a plurality of micropores in at least one of the high performance elastomer portion and the low performance elastomer portion of the film.
In accordance with one particularly preferred embodiment, the films of this invention are produced by blending or compounding a filled styrenic block copolymer with a filled polyolefin, forming a blended or compounded product, forming the blended or compounded product into a filled film comprising a well dispersed blend of styrenic block copolymer and the polyolefin, and stretch-thinning the film, forming a plurality of micropores throughout the stretch-thinned film.